a. Field of the Invention
This invention relates to ionizing gas guns or nozzles in which a stream of air or other gas is blown over corona discharge electrodes internally enclosed within the nozzle to forcibly direct positive and negative ions emitted thereby against targeted articles or objects in order to effect static neutralization thereof. More particularly, this invention pertains to ionizing air guns or nozzles intended for use in ultra-clean environments wherein an inert gas, such as nitrogen, can be employed as the medium for spraying the dual polarity ions against the surface of the articles. The novel concepts of the present invention are intimately related to assuring that the dual polarity ion emission is always balanced in the production of positive and negative ions.
b. Prior Art
U.S. Pat. No. 3,156,847 and No. 3,179,849 show examples of ionizing air guns or nozzles in which air is blown over a discharge electrode coupled to an A.C. high voltage power source wherein a stream of dual polarity ions is forcibly directed against charged articles in order to statically neutralize such articles and any particles on the surface thereof.
In U.S. Pat. No. 4,423,462, No. 4,093,543, No. 3,714,531 and No. 2,879,395 are shown various systems for controlling or equalizing the ratio of positive and negative ion emission, which is ordinarily unbalanced because of the geometry of the particular static bar construction, including whether the discharge points were directly or capacitively coupled to the A.C. high voltage generator.
For ultra-clean room applications, where submicroscopic dust and microparticulate contaimination is of major consideration in the manufacture and/or assembly of components, such as semiconductor substrates, compressed nitrogen has often been used as the blowing medium because of its inert character and greater facility to ionize under the high voltage field at the discharge points. For the use of nitrogen as the blowing gas in ionizing gas guns and nozzles, see U.S. Pat. No. 4,027,686 and No. 4,132,567.
Also of considerable significance for efficient operation within ultra-clean rooms is the need to provide chemical inertness of the gun material as well as the desirability to reduce the weight and cost of the gun per se. Thus, it would appear appropriate to utilize plastics for the gun body and avoid the use of metal as much as possible. However, because of the non-conductive nature of plastic materials generally, there is no convenient way to provide a proximity ground for producing, as in a conventional A.C. static neutralizer, a high intensity field between the discharge points and ground. It therefore becomes necessary to utilize a double D.C. approach wherein positive and negative discharge electrodes are respectively coupled to corresponding positive and negative high voltage power supplies (i.e., the field being produced between the electrodes of opposite polarity rather than between each electrode and ground). Pat. No. 4,333,123 discloses an ionizing air gun having an all non-conductive housing enclosing first and second discharge tips which are connected to respective D.C. high voltage sources along with extended barriers to inhibit ion recombination thus extending the neutralizing range.